Shell,one thing your knee can do for you is to encourage you to get in the best shape possible, despite the knee. I know that for my two foot and one knee operations, I had to get tested extensively each time, to make sure I was up to an operation. So be in the best shape you can be in so that when the time comes...you are ready. And being in shape, even before your knee operation, will help you in life...it's a win/win situation.
We need as many win/win situations as we can get so grab this one.